A British man believed to have knowledge of missing Madeleine McCann reportedly fled NSW after being convicted of child sex offences in the late 1990s.

British media is reporting that 76-year-old Roderick McDonald will be questioned by UK police about a possible pedophile ring linked to the three-year-old's disappearance in Portugal more than seven years ago.

McDonald, known as Roderick William Robinson while in Australia, has previously been convicted of a number of sex offences, and received a six-month sentence for the sexual assault of a nine-year-old girl in Sydney in 1998-1999, the Daily Telegraph has reported.

He was arrested by police at Sydney Airport in 2001 on three charges but fled the country on bail and spending years on the run before being arrested in Portugal.

After being extradited in Australia, he pleaded guilty to two counts of indecent assault of a child under 10, and served his sentence.

McDonald has been on the run again since being convicted in 2012 of abusing two girls, was arrested and is being held in Malta, London's Daily Mirror reports.

He will be deported back to England to serve his prison sentence and will also face questions by detectives investigating Madeleine's disappearance from a hotel in Portugal in 2007.

McDonald is said to be a "notorious" pedophile and was known to have been in Portugal at the time of Madeleine's disappearance but has never been interviewed by police, The Mirror reports.

The newspaper says McDonald was once extradited to Australia to face charges of raping an eight-year-old girl.

He reportedly received a six-month jail sentence after pleading guilty and after being freed he left the country for Thailand.